1. Field of the Invention
This invention relates in general to a method and apparatus for accurately positioning the magnetic write/read head of a disk drive, and more particularly, to a method and apparatus for accruately positioning write/read heads which provide a write gap and a shorter read gap relative to a recording medium having concentric data tracks and radial burst patterns recorded thereon for determining the position of the heads, wherein a second position signal is detected before a first position signal is discontinued.
2. Description of Related Art
On a magnetic disk such as a hard disk or a flexible disk, a plurality of data tracks is concentrically formed. When information is read from or written to the magnetic disk, the magnetic head is moved in the radial direction of the magnetic disk to face a specific data track (a so-called seek operation), and thereafter an information reading or writing operation is performed with respect to the specific data track.
The positioning of the magnetic head for causing the magnetic head to face the specific data track is performed by reading a burst pattern continuously recorded in the radial direction of the magnetic disk. For example, FIG. 9 (a) illustrates a typical burst pattern recorded on a magnetic disk.
In FIG. 9 (a), the magnetic disk rotates in the circumferential direction of the magnetic disk (the direction of arrow A in FIG. 9), and a magnetic head (not shown) moves in the radial direction of the magnetic head (the direction of arrow B or the opposite direction in FIG. 9). On the magnetic disk, a plurality of data tracks on which data is recorded 54N (N is a positive integer), 54N.+-.1, 54N.+-.2, 54N.+-.3, . . . , are concentrically formed, and a burst pattern 902 is recorded in the radial direction of the magnetic disk. The burst pattern 902 consists of a first burst pattern train 910 formed by arranging in the radial direction regions 912 in which data is recorded, a second burst pattern train 920 similarly formed by arranging in the radial direction regions 922 in which data is recorded, a third burst pattern train 930 similarly formed by arranging in the radial direction regions 932 in which data is recorded, and a fourth burst pattern train 940 similarly formed by arranging in the radial direction regions 942 in which a signal is recorded.
The size of each region constituting the burst pattern trains 910 and 920 in the radial direction of the magnetic disk is made to equal to the pitch (P) 960 of the data tracks, and these regions are staggered in the radial direction of the magnetic disk so that both edge sections thereof in the radial direction coincide with the central position of each of the data tracks. Also, the size of each region constituting the burst pattern trains 930 and 940 in the radial direction of the magnetic disk is made to equal the pitch (P) 960 of the data tracks, and these regions are staggered in the radial direction of the magnetic disk so that both edge sections thereof in the radial direction coincide with the central position between the respective data tracks.
If the burst pattern is read while the magnetic head is moved in the radial direction of the magnetic disk, a position detection signal is obtained. The position detection signal includes two types of signals. A first composite signal A/(A+B) is obtained by dividing the signal obtained by reading the first burst pattern train 910 (hereinafter referred to as signal A) by the signal obtained by adding to the signal A, a signal obtained by reading the second burst pattern train 920 (hereinafter referred to as signal B), and a second composite signal D/(C+D) which is obtained by dividing the signal obtained by reading the fourth burst pattern train 940 (hereinafter referred to as signal D) by the signal obtained by adding to signal 940, a signal obtained by reading the third burst pattern train 930 (hereinafter referred to as signal C).
The position detection signal A/(A+B) changes linearly when the gap center passes near the center of the data track 54N in the width direction thereof (the direction of arrow B in FIG. 9). Incidentally, the position detection signal A/(A+B) also changes similarly when the gap center passes the center of other data tracks 54N+1, 54+2, 54N+3, . . . in the width direction thereof. Also, the position detection signal D/(C+D) changes linearly when the gap center passes near the center between the data track 54N and 54N+1. In addition, the position detection signal D/(C+D) also changes similarly when the gap center passes near the center between other data tracks 54N+1, 54N+2, 54N+3, . . . .
Accordingly, based on the levels of the position detection signals A/(A+B) and D/(C+D), the position of the gap, namely, the position of the magnetic head can be determined and, based on the levels of the position detection signals, the magnetic head can be positioned so that the gap center is positioned at the center of the width of the data track. Thus, before the position of the magnetic head reaches the data track 54N+1 from the data track 54N, the position detection signal A/(A+B) is switched to the position detection signal D/(C+D) so that the position signal is not discontinued and the magnetic head can be positioned based on the position detection signal level.
More recently, magnetic heads have been proposed which read information using a magnetoresistance element (hereinafter referred to as an MR element). The MR element is an element which utilizes the magnetoresistance effect. Thus, if a semiconductor is placed in a magnetic field, the direction in which the electrons or positive holes in the semiconductor advance is changed by the magnetic field, whereby the traveling path becomes longer and the resistance value increases. In the magnetic head which uses the MR element to read information and uses a coil to write information, there are provided separately a read gap and a write gap. However, the longitudinal size of the read gap is shorter than the write gap. Accordingly, data is written wide and read narrow to decrease the crosstalk from other data tracks, thereby obtaining a position detection signal having a small S/N ratio. Thus, the recording density may be increased.
However, when the longitudinal size of the read gap is shortened and the read range is shortened as described above, a region 970 occurs in which the position detection signals A/(A+B) and D/(C+D) cannot be detected, as shown in FIG. 9 (b). If such a region 970 occurs, the position at which the magnetic head is currently located cannot be determined, and the magnetic head cannot be positioned.
In FIG. 9 (b), the abscissa represents the position of the magnetic head and, more specifically, the longitudinal center position (center) of the gap formed in the magnetic head.
If, on the one hand, the read range is widened to solve such problem, the primary object, writing data wide and reading it narrow to increase the recording density, cannot be accomplished.
On the other hand, as disclosed in PUPA No. 4-353679 official gazette, a burst pattern consisting of four special burst pattern trains formed by the respective regions having their length in the radial direction of the magnetic disk made shorter than the pitch of data tracks is prerecorded on the magnetic disk to solve the above problem. From a total of eight signals obtained by calculating the four signals obtained from the burst pattern, a single signal to be used as the position detection signal is switched according to the magnetic head position, thereby obtaining a position detection signal which changes linearly over a wide range of movement for the magnetic head.
Nevertheless, in the above approach the determination of signal switching and processes such as the calculation for obtaining a position detection signal is cumbersome. Further, the above approach requires the recording of a special burst pattern on the magnetic disk, in which special burst pattern the length of the respective regions in the radial direction of the magnetic disk is shorter than the pitch of the data tracks. Thus there is a problem in that labor and time must be taken to record the burst pattern. In addition, the above official gazette discloses that the addition or subtraction of a predetermined bias value with relation to the obtained signal can provide a position detection signal which changes linearly for movement of the magnetic head. However, the offset changes according to the voltage supplied to the magnetic head or the ambient temperature and, thus, even if a fixed value is given as the bias value, an unnatural section, or a so-called point of inflection, occurs in the position signal at a point where the signal used as the position detection signal is switched.
It can be seen then that there is a need for a magnetic head positioning method and apparatus wherein the positioning of the write magnetic head and the read magnetic head can be performed reliably.
It can also be seen that there is a need for a magnetic head positioning method and apparatus wherein data is written wide and read narrow to decrease the crosstalk from other data tracks, but gaps between regions which generate position detection signals are prevented.